Evidence for modification of nickel oxide by silica. Infrared, electron microscope and dissolution rate studies

Infrared spectroscopic evidence for marked interaction between nickel oxide and silica at temperatures as low as 550°C is described. An infrared absorption at approximately 1045 cm–1 can be attributed to silicon atoms in the nickel oxide lattice. This is observed in both annealed nickel oxide + silica mixtures and nickel oxide heated in silica tubes. Electron microscopy shows that the nickel oxide particles (with incorporated silicon) are single phase. The silicon content produces a surface morphology which becomes predominantly {111}. Dissolution rates per unit surface area in dilute acid are decreased more than one hundred times by the interaction, even with < 10–3 mol % silicon in nickel oxide. The slower dissolution is found throughout dissolution. The silicon atoms apparently enter the tetrahedral interstices in the oxygen lattice, effectively producing SiO4 groups. The work shows that adsorption and catalytic studies of nickel oxide surfaces are markedly affected by the presence of silica even for samples pretreated at relatively low temperature